Webcam resource validation + first-frame proof + CameraConflictProbe: MediaCaptureFrameSource validates post-init (VideoDeviceId match, stream properties, reader StartAsync status), subscribes Failed/CameraStreamStateChanged → SourceFailed; CameraManager.AcquireAsync requires first-frame proof (4s timeout) — silent empty box impossible; MainViewModel surfaces WebcamError chip + MessageBox with suspect-app names; fallback ladder VideoPreview → VideoRecord; 19041 SDK projection gaps documented; AGENTS.md + schema.md + HANDOFF.md memory-map rules added; 81 tests passing, 0 warnings

Helpers/CameraConflictProbe.cs

@@ -0,0 +1,47 @@
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+
+namespace ytLive.Helpers;
+
+/// <summary>
+/// Best-effort diagnostic: when a camera won't start, lists other running
+/// processes known to hold cameras (OBS, Zoom, Teams, NVIDIA Broadcast, etc.).
+/// Windows doesn't expose "which process has this device" via any public API,
+/// so this is a suspect list, not a verdict — but it's far better than
+/// "maybe in use by another app" with no idea which one.
+/// </summary>
+public static class CameraConflictProbe
+{
+    private static readonly HashSet<string> KnownCameraApps = new()
+    {
+        "obs64", "obs32", "zoom", "teams", "ms-teams", "discord",
+        "nvidia broadcast", "skype", "webex", "slack",
+        "streamlabs obs", "restream studio", "manycam", "snap camera",
+        "logitech capture", "logitune", "facerig", "animaze",
+        "camera", "vmix", "xsplit broadcaster", "xsplit gamecaster",
+        "droidcam", "ivcam", "epoccam", "camo",
+        "chrome", "msedge", "firefox", "brave",
+    };
+
+    /// <summary>
+    /// Returns the friendly names of known camera apps currently running, or an
+    /// empty list if none are found (or the probe itself fails).
+    /// </summary>
+    public static List<string> GetRunningCameraApps()
+    {
+        try
+        {
+            return Process.GetProcesses()
+                .Where(p => KnownCameraApps.Contains(p.ProcessName.ToLowerInvariant()))
+                .Select(p => p.ProcessName)
+                .Distinct()
+                .OrderBy(n => n)
+                .ToList();
+        }
+        catch
+        {
+            return new List<string>();
+        }
+    }
+}

Helpers/index.md

@@ -12,6 +12,7 @@ Cross-cutting utilities. See [`schema.md`](../schema.md) for the memory-map conv
 | `TokenStore.cs` | DPAPI-protected OAuth session persistence (`%APPDATA%\ytLlive\ytLlive.auth`, CurrentUser scope); `Save`/`Load`/`Clear` — sign-in survives restarts |
 | `ImageCache.cs` | Image byte caching (assets live in the DB) |
 | `InverseBoolToVisibilityConverter.cs` / `NotNullToVisibilityConverter.cs` | XAML value converters for visibility bindings |
+| `CameraConflictProbe.cs` | Best-effort diagnostic: when a camera won't start, enumerates running processes known to hold cameras (OBS, Zoom, Teams, NVIDIA Broadcast, browsers, etc.) — Windows doesn't expose "which process has this device" via any public API, so this is a suspect list, not a verdict |
 
 Related: [`Themes/Controls.xaml`](../Themes/Controls.xaml) styles the lists this
 class backs; [`Models/index.md`](../Models/index.md) and